This invention relates to integrator circuits and more particularly to an integrator circuit that utilizes a current mirror circuit in combination with at least two current sources to separate vertical sync pulses from horizontal sync pulses in a television (TV) receiver.
A typical TV receiver separates the vertical sync pulses from the horizontal sync pulses by passing the composite sync waveform through an integrator circuit which smoothes the narrow horizontal sync pulses and provides a rapidly rising voltage for the broad sync pulses. A slicer set to about one-half the pulse height provides a sharp output pulse to synchronize the vertical deflection system.
More TV receivers are being fabricated with one or more integrated circuits. In order to save pin-outs on the integrated circuitry and to eliminate relatively expensive external discrete components, it is desirable that passive components, such as the integrator capacitance, be incorporated into the integrated circuit. It is also desirable for a vertical sync separator circuit to have different time constants for charge and discharge of the capacitor under different received signal conditions to improve noise performance.
Accordingly, one object of this invention is to provide an improved integrator circuit for separating vertical sync signals from horizontal sync signals in a TV receiver.
Another object of this invention is to provide an integrator circuit that can be readily fabricated in an integrated circuit.
A further object of this invention is to provide an integrator circuit having a time constant that varies with the magnitude of the signal applied thereto.
Still another object of this invention is to provide an integrator circuit having different time constants for charging and discharging a capacitor.